Signal is exploring the use of zero-knowledge proofs (ZKP) to enable user registration without requiring a phone number, according to community discussions on the Signal user forum.
Zero-knowledge proofs are a cryptographic technique that allows verification of information without revealing the actual data. According to the forum discussion, Signal already uses this technology for donation badges, backup payments, and group functionality. The technology can verify details like username character length and content restrictions without exposing the username itself.
The approach aligns with Signal’s broader design philosophy. As one community member noted, “the great thing about Signal is the client is designed to already not trust the server.” This means the system is built to protect user privacy even without examining server code.
However, significant questions remain unresolved. Community members raised concerns about whether phone numbers would be completely unlinked from usernames under this system, and what data remnants might persist locally on devices or on Signal’s servers. One participant suggested that full unlinking may not be entirely possible, raising the question of whether new accounts created without a phone number from the start might be preferable to unlinking phone numbers from existing accounts.
Spam and account abuse pose another challenge. If users could unlink phone numbers for free, bad actors could potentially register with a single number, unlink it, and repeat the process to create unlimited accounts. Community members suggested implementing a cooldown period between unlinks as a mitigation strategy, though debate continued over whether even a month-long cooldown would adequately prevent spam and scams.
The feature remains in discussion stages. Signal has not confirmed implementation or released technical specifications. Community members called for Signal to clarify technical details around privacy protections if the feature moves forward. The organization has not yet provided official statements addressing the specific concerns raised about phone number unlinking, data remnants, or anti-spam measures.
Key facts
- Signal is considering using zero-knowledge proofs to allow registration without a phone number
- The technology is already used by Signal for donation badges, backup payments, and group features
- Key questions remain about complete phone number unlinking and data retention
- Spam prevention through cooldown periods was suggested as a possible control mechanism
- The feature has not been officially confirmed or implemented by Signal